This study will explore the safety and effectiveness of different doses of AGN 203818 in relieving Irritable Bowel Syndrome pain. The study is being conducted in 2 parts. Part A enrolled 213 pts dosed with either 3, 20, 60 mg AGN 203818 or placebo over 4 week treatment duration. Part B will enroll 320 pts and dose with either 60, 100, 160 mg BID AGN 203818 or placebo over 12 week treatment duration.